1. Field of the Invention
This invention relates to a heat-fixing silicone rubber roller used in copying machines, laser beam printers, fax machines and so forth. More particularly, it relates to a fixing silicone rubber roller having a silicone rubber layer provided on its outer periphery with a fluorine resin layer and/or a fluorine rubber layer.
2. Description of the Prior Art
As fixing rollers used in copying machines, laser beam printers, fax machines and the like, conventionally used are silicone rubber rollers comprising a roller shaft (a mandrel) and a silicone rubber surface layer provided on the former's outer periphery. This is because silicone rubber has toner releasability, heat resistance, compression set and so forth which are superior to those of other rubber materials.
In recent years, as machinery of this type has been made high-speed, oil fusing which feeds silicone oil to the surface of a fixing roller is carry out for the purpose of improving toner releasability. Also, rubber materials are being made to have low hardness so that, at the time of high-speed fixing, fixing width (nip width) can be ensured to increase the time taken for fixing.
However, since the silicone rubber has originally the same quality as the silicone oil and moreover has been made low-hardness, there is a problem that it may be swelled with the silicone oil fused. As a means for solving this problem, fluorine resin and/or fluorine rubber is/are further provided by coating, on the surface of a silicone rubber roller whose surface layer is formed of a silicone rubber or silicone rubber foam having a low hardness, or the above silicone rubber layer is covered with a fluorine resin tube to provide a fluorine resin layer on the outer periphery of the silicone rubber layer.
Such a means brings about a remarkable improvement in service life as fixing rollers. However, the coating of fluorine resin requires a high temperature exceeding the melting temperature of fluorine resin. Also, the coating of fluorine rubber requires high-temperature baking carried out at 300 to 350.degree. C. for 15 minutes to 1 hour after coating. In such a condition of high temperature, however, the silicone rubber layer may deteriorate in part to damage adhesion between the fluorine resin layer or fluorine rubber layer and the silicone rubber layer. Moreover, the fixing roller thus obtained has had a problem on durability. The silicone rubber roller covered with a fluorine resin tube to provide a fluorine resin layer on the outermost layer also has had a problem that the fluorine resin layer (tube) and silicone rubber layer may come off with an increase in the number of paper feed. In particular, those having a low-hardness silicone rubber layer may greatly cause these problems. Accordingly, it has been a pressing need to make development of a fixing silicone rubber roller having a coating layer of fluorine resin and/or fluorine rubber, which has both superior interlaminar adhesion and superior durability.